Question: What minimum triangular number has an instance of which composite number?
Paraphrase: What least triangular number has an occasion of which composite number?
SPARQL (Wikidata): select ?ent where { ?ent wdt:P31 wd:Q245102 . ?ent wdt:P1181 ?obj . ?ent wdt:P31 wd:Q50707} ORDER BY ASC(?obj)LIMIT 5 
Answer: 6, 10, 15, 21, 28